The present invention relates to a rotary printing press in general, and more particularly to a drive for an ink supplying device of such a press.
Rotary printing presses are well known and in widespread use, particularly in the printing industry so that it is not necessary to dwell on the details of such presses. Suffice it to say that such machines include plate cylinders which carry the plates on which the images that are to be printed on an advancing web are formed, a blanket cylinder being interposed between the respective plate cylinder and the advancing web and serving to transfer the ink replica of the image from the plate cylinder to the advancing web. The printing ink for the replica is supplied to and appropriately distributed over the plate cylinder by an ink supply device which is constituted by a plurality of distributing, transfer and application rollers that are in respective contact with one another and with the plate cylinder. The printing image is often delivered to one of the distributing rollers from an ink supply roll of an ink supply fountain by a ductor roll, which is a roll mounted not only for rotation but also for displacement between two positions in one of which it contacts the ink supply roll to be replenished with the printing ink thereby, and in the other of which it contacts the one distributing roller to deliver the printing ink thereto. Then, a drive is provided for driving the distributing rollers, the plate and blanket cylinders, the displacing arrangement for the ductor roll, and the ink supply roll, or several individual drives may be provided for separately driving selected ones of the above-mentioned components. The drives are of different constructions, some of which will be presently discussed in connection with a rotary printing press of the above-discussed type. However, it will be appreciated that the drive of the present invention and the associated ink supplying device may also be used in other types of rotary printing machines.
It is also well known that, in the above-discussed ink supplying device, the ink supply roll rotates relatively slowly while the distributing roller with which the ductor roll comes into contact when delivering the ink thereto in the other of the above-discussed positions rotates at a relatively high peripheral speed which actually corresponds to the speed of advancement of the advancing web. The ductor roll itself is not being driven in rotation but rather is entrained by the ink supply roll during the short-lived rolling contact therewith while the ductor roll is in its replenishing position. While in such a rolling contact, the ink supply roll delivers a narrower or a wider strip of the printing ink to the ductor roll. On the other hand, when the ductor roll reaches the delivering position thereof, for a short period of time, it will be entrained for a rolling contact with the above-mentioned distribution roller for rotating at a peripheral speed which considerably exceeds the peripheral speed which the ductor roll has acquired during its contact with the ink supply roll. While in contact with the distributing roller, the ductor roll will deliver the printing ink to the distributing roller from where the printing ink will be transmitted to the remaining transfer, distributing and application rollers until it reaches, in the desired distribution and other conditions, the plate roller.
It will be appreciated that when the ductor roll rotating at a relatively low peripheral speed is entrained by the distributing roller with which it comes into contact in the delivering position thereof for rotation at a much higher peripheral speed, there will come into existence a jolt resulting from the sudden energy demand needed for the rapid acceleration of the ductor roll, which leads to a multitude of unpleasant phenomena well known to those familiar with the printing industry, most, if not all, of which adversely affect the printing quality.
This problem has already been recognized before, and some solutions either partially or fully avoiding this problem have already been proposed. So, for instance, in the U.S. Pat. No. 3,002,451, the driving connection between the printing cylinders and the rollers of the ink supplying device is made relatively elastic by using roller-equipped chains or the like. However, this solution is only partial inasmuch as it only brings about a certain damping of the above-mentioned driving jolt.
To reduce the adverse affects of the above-mentioned jolt to the greatest feasible extent, it has been already proposed in the German published patent application DT-OS No. 20 31 504 to so construct an ink supplying device of a rotary printing press as to include a motor for accelerating the ductor roll. Thus, the ductor roll is accelerated during its displacement from the replenishing into the delivering position by a separate driving roll which is in a frictional contact with the ductor roll in such a manner that the jolt to which the ink supplying device is subjected at the moment of contact of the ductor roll with the associated distributing roller is reduced to a minimum.
However, this construction suffers of several drawbacks. One of the problems encountered in this arrangement is the relatively high manufacturing and even operating cost of this arrangement. On the other hand, it is a disadvantage of this arrangement that the driving roll which is associated with the ductor roll is located outside of the path of flow of the printing ink and thus acts as an undesired ink storage. Thus, as a result of the provision of this separate and additional driving roll, the ink supplying device becomes undesirably sluggish as to the possibility of desired or necessary changes in the amounts and exact color of the printing ink. In other words, any adjustments and changes attended to at the ink measuring or metering arrangement will reflect in the quality of the printed matter only after a considerable period of time.
In order to avoid this disadvantage, the U.S. Pat. No. 3,688,696 proposed to so construct the accelerating drive that the motor which drives the ductor roll by means of two V-belts, is put into action only when the ductor roll dissociates itself from the ink supply roll. This patent reveals that the speed of the motor is to be so controlled during the displacement of the ductor roll that the latter achieves a relatively high peripheral speed before it reaches and contacts the respective distributing roller. A speedometer is connected to the motor and is operative for discontinuing the operation of the motor when the latter has achieved a certain number of revolutions per minute.
However, even this arrangement is disadvantageous in several respects. First of all, even this arrangement is rather expensive both in terms of material and labor expense. Furthermore, when the rotary printing press is operated at the speeds which are usual nowadays, the full cycle of displacement of the ductor roll takes only about 0.5 seconds. Thus, the acceleration phase, which coincides at least with a greater part of the displacement of the ductor roll between the ink supply roll and the respective distributing roller, lies in the range of one-tenth of a second. Thus, it will become evident that there will be a high loading, especially of the motor and, based thereon, a high probability of even frequent malfunctions cannot be avoided.